The present invention relates to a method of cutting grooves in a ceramic hydrodynamic bearing which is suitably used as radial and thrust bearings for a rotating member that rotates at high speed.
Recently, with the increase in the speed of spindle motors for HDDs (Hard Disk Drivers), radial and thrust bearings of high performance have been demanded, and employment of ceramic hydrodynamic bearings has been proposed as one technique to meet the demand. In the ceramic hydrodynamic bearings, it is essential to minimize the absolute value of the number of fine particles generated from the sliding surface.
Hitherto, shot blasting process has been mainly employed as a method of cutting hydrodynamic pressure generating grooves in the sliding surface of such a ceramic hydrodynamic bearing.
However, if groove cutting is effected by shot blasting process, cuticles (pineal) 2b are formed on the surface of the machined portion, that is, the portion formed with a hydrodynamic pressure generating groove 2, as shown in FIG. 3, so that the abrasive or cuttings are caught between the cuticles 2b and it is not easy to wash them off. The abrasive or cuttings that are left unremoved by washing constitute a large source of generation of fine particles. Meantime, cuticles themselves, which are likely to separate, constitute a source of generation of fine particles. In addition, a large number of microcracks are generated under some shot blasting conditions, and these microcracks invite an increase in the amount of fine particles.
JP. A, 58-179588 discloses a method of forming grooves in a ceramic hydrodynamic bearing wherein a laser beam is irradiated only to the required place to form the grooves. The burrs at circumferential edges of each groove are removed by finishing after forming grooves.